Central to the provision of Air Traffic Control (ATC) services within the National Airspace System (NAS) are three major functions; these are navigation, surveillance and communications. Navigation allows aircraft to navigate along assigned routes. Surveillance allows the collection of information as to aircraft position. Air-ground communications facilitates the delivery of ATC instructions to airborne pilots, and the receipt of data and requests from pilots. The NAS has an extensive existing infrastructure to support these major ATC functions.
To support navigation the nation is covered with a network 959 VHF Omnidirectional Ranges (VOR). VORs provide the signals in space which are the principal support for aircraft navigation in the enroute and terminal environments. VORs are supplemented with Distance Measuring Equipment (DME), LORAN C, and to an increasing extent the Global Positioning System (GPS). To support instrument landing approach navigation, the nation's airports are equipped with 797 Instrument Landing Systems.
Surveillance needs are met by the maintenance of a network of primary and secondary radar systems. This network is made up of 298 primary radars and associated secondary radar sensors and approximately 30 secondary radar-only surveillance sites.
The air-ground communication function is supported through a network of VHF and UHF radios with terminations at the enroute, terminal, tower, and flight service station control positions requiring direct communications with pilots.
The ATC system supported by the navigation, surveillance, and communications infrastructure described above is the primary system used to establish and maintain safe separation between aircraft participating in the ATC system and between these aircraft and the ground. As a backup to this system, the FAA has developed and aircraft are equipped with the Traffic Alert and Collision Avoidance System (TCAS). This system uses data received from airborne transponders responding to secondary radar interrogations and is the last line of defense against unsafe air traffic situations.
While effective, the existing NAS ATC infrastructure has many problems. These problems include:
Very high level of operations and maintenance expenditure required to maintain the vast network of navigation, surveillance and air-ground radio equipments. PA1 Insufficient spectrum is available in the VHF-band to accommodate needed requirements. Currently, this spectrum is used by air-ground radios, VORs, and the localizer component of instrument landing systems. Lack of available frequencies is becoming a limiting factor in the expansion of ATC services. PA1 Very high replacement costs for aging surveillance, navigation, and air-ground radio components. PA1 High channel noise experienced in current analog radio technology. PA1 Limited capability for effective communications network management and control allowed in analog communications technology. PA1 Limited surveillance accuracy resulting in data insufficient for the purposes of advanced ATC algorithms. PA1 Limited directional differentiation in TCAS resulting in high false alarm rates and data not readily supportive of resolution algorithms. PA1 Nonexistence of an air-ground data communications capability resulting in air-ground frequency congestion, high controller workload, and error prone air-ground communications. PA1 SACOM will eliminate the need for expenditure for replacement of aging ATCBI systems and an eventual need to modernize or replace VOR equipment. PA1 SACOM reduces infrastructure O&M cost through the elimination of the need to maintain the extensive network of VORs and secondary surveillance sensors. PA1 SACOM releases valuable VHF spectrum currently being used by the VOR infrastructure. PA1 SACOM provides for high quality digital voice greatly reducing channel noise currently experienced by pilots and controllers. PA1 SACOM allows the increased level of communication network monitoring and control facilitated by digital technology. PA1 SACOM provides an air-ground data link capable of supporting two-way data link capability and the ATN concept. PA1 Integrated VHF/UHF voice channels for commercial and military ATC (they are separate now)--doubles capacity. PA1 8M/2.sigma. three dimensional accuracy for: PA1 Faster position reporting update rate. PA1 Data link on average provides 5 Kbps. PA1 Data link ATN compatible. PA1 In control sectors requiring greater throughput, additional data channels can be added. PA1 Unique digital data and position reporting protocol--no garbling of position report or data anywhere.
The object of this invention is to provide an integrated ATC communications, navigation, and surveillance infrastructure to eliminate the above cited problems.
The invention is directed to an integrated communications, navigation surveillance system which overcomes the problems in the current NAS described above. A major feature of the invention is a new air-ground radio infrastructure operating in the existing VHF and UHF bands: a pair of frequencies is associated with each air traffic control position. One of the frequencies will support party line voice for the air traffic sector consistent with the current ATC operational concept. The second frequency will support a data channel to be used for downlinking dependent surveillance data and for both uplink and downlink data communications consistent with current FAA two-way data link operational concepts. Frequencies will be paired so that each time a frequency change is commanded by the ground, both the voice and data channel will be tuned to the new air-ground frequency pair. In a preferred embodiment of the invention, supporting radios are to be all digital, operating with 12.5 kHz spacing. VFR aircraft not receiving ATC services will be supported with a common access channel and separate data channels to allow surveillance data collection from the aircraft without a change in the operational concepts present in today's ATC system.
The term SACOM as used herein refers to applicants' surveillance and communication system of this invention used in an air traffic control system.
The SACOM system employs dependent surveillance to provide data to meet surveillance requirements. The SACOM navigational data source will be the Global Positioning System (GPS) as augmented by the FAA to allow GPS as a sole means of navigation. The SACOM system, in a preferred embodiment employs triply redundant GPS receivers with majority voting to ensure, with high probability, that the aircraft position reported over the SACOM data channel will be suitable for air traffic control purposes. The SACOM data link structure provides for 3D position reporting with a 6-second surveillance update rate for up to 60 aircraft for each enroute air traffic control position and 3-second surveillance update for up to 30 aircraft for each terminal air traffic control position. Position reports will be made available to requiring ground systems through a terrestrial network providing for the distribution of these data. Position reports will be made available to TCAS systems through RF front ends which will allow monitoring the multiple data link frequencies of interest for a given geographical area.
The SACOM system is consistent with the Aeronautical Telecommunications Network (ATN) protocol architecture. Airborne components are designed to fit into modern aircraft data architectures. The principal supporting ground component in addition to the air-ground radios is the SACOM Communication Controller (SCC). This component formats uplink data and provides for the separation of downlinked surveillance data from general communications data. The surveillance data is disseminated to the requiring ATC processors in accordance with static routing tables. The communications data is interfaced to the ATN at the network protocol layer via the ATN routing function.
The system of this invention solves the problems cited with the existing communications, navigation, surveillance architecture as follows:
A summary of the major technical benefits of the preferred embodiments of the invention are as follows:
12.5 Hz digital voice channels--VHF/UHF--doubles number of channels.
12.5 Hz digital 3D position reporting and data link channels--VHF/UHF.
Surveillance everywhere. PA2 TCAS target reports. PA2 Terminal surface. PA2 6 seconds enroute. PA2 3 seconds terminal.